1. Field of the Invention
This invention relates, in a general way, to resonators and oscillators for their implementation. More specifically, the invention relates to high-stability resonators and oscillators in the low and medium frequency range.
2. Description of the Prior Art
The currently most efficient high-stability oscillators mainly use resonators in piezoelectric material, principally quartz. Other piezoelectric materials such as berlinite are also used. In this type of resonator in piezoelectric material, the piezoelectric effect is an easy means for converting the energy from an electric field applied to the piezoelectric material into mechanical work. For high-stability quartz resonator oscillators, the relative frequency deviation is at best in the region of 10.sup.-10. In the case of the "down-market" quartz resonator oscillators widely used in electronic equipment, the relative frequency deviation is between 10.sup.-5 and 10.sup.-7. This relative frequency deviation is largely due to the resonator time drifts and depends on environmental conditions such as temperature.
The quartz resonator drifts are partly inherent to the material used, i.e. quartz. Tests have shown up the limitations of quartz which is the best of the known piezoelectric materials. Quartz, and all crystalline materials in general, have structure defects and impurities in the interstitial channels. The relative mobility of these impurities in the interstitial channels provokes frequency time drifts and excessive sensitivity to ionizing radiations, particularly when the quartz is excited in the flexural mode. High-stability quartz resonators require the use of very high quality quartz. It is becoming difficult at present to find natural quartz of sufficiently high quality. The synthesis of artificial quartz has not been fully mastered.
Furthermore, the sensitivity of quartz to temperature variations imposes the use of expensive thermostat-fitted enclosures for these high-stability oscillators.